m class Solution {
public:
    bool containsNearbyDuplicate(vector<int>& nums, int k) {
        unordered_map<int, int> m;
        for (int i = 0; i < nums.size(); ++i)
        {
            if (m.count(nums[i]) && abs(i - m[nums[i]]) <= k) return true;
            m[nums[i]] = i;
        }
        return false;
    }
};